because \((A^{k})_{ij}\)  represents the number of walks with \(k\)  hops between
node \(i\)  and node \(j\)  (see [1]}). From
(REF ), (REF ) and
\(d_{i}=(Au)_{i}=(A^{2})_{ii}\) , we have
\(\left|\mathcal {N}_{i}\setminus \mathcal {N}_{j}\right|=\left(A^{2}\right) _{ii}-\left( A^{2}\right) _{ij}\) 
